In situ generated FeF₃ in homogeneous iron matrix toward high-performance cathode material for sodium-ion batteries

A strategy for enabling highly insulated FeF₃ as high performance cathode materials for NIBs is proposed and realized, through constructing metallic Fe and reduced graphene oxide (RGO) double enhancement conducting matrix, wherein both the metallic Fe and active FeF₃ are in situ electrochemically generated from one FeF₂ grain (as precursor of FeF₃) to ensure their desired homogenous and intimate contact. The efficacy of this concept is demonstrated by the superior electrochemical performance of the generated FeF₃-Fe-RGO composite including high capacity of 150mAhg^-1 at a current density of 50mAg^-1, good cycle stability, and high power capability at room temperature, which could be reasonably attributed to homogeneous conductive matrix composed of metallic Fe and RGO in the composite and especially their ideal contact with the active FeF₃ component. The strategy is simple yet very effective and also because of its versatility, it may be easily extended to other next generation high-capacity electrode materials while with low electrical conductivity.